1. FIELD OF THE INVENTION
This invention relates to an analyzer, and more specifically to a highly reliable sampler for exhaust gases.
It is known that the dilution of the gas sample is essential for the analysis of exhaust gases, such as flue gases with high dust concentrations or highly concentrated sulfurous acid gases, by means of an aerosol monitoring instruments, flame intensity type SO.sub.2 analyzer or the like which can analyze only the gases containing smoke dusts (particulates) or SO.sub.2 in low concentrations.
Also, when measuring the dust content of flue gases, it is imperative to sample the gases by so-called synchronized suction, or at the rate of suction in the inlet of the nozzle made equal to the flow velocity of the gases.
The present invention is concerned with an exhaust-gas sampler which can easily accomplish the dilution and synchronized suction to meet the foregoing requirements.
2. DESCRIPTION OF THE PRIOR ART
Prior art arrangements will now be described, by way of exemplification, in connection with aerosol monitoring.
As is known in the art, aerosol is a system consisting of a gas in which fine solid or liquid particles are suspended. Attempts have recently been made to utilize aerosol monitoring instruments of the light scattering type for continuous automatic measurement of the dust content of flue gases. The measuring instruments for this purpose are called stack dust monitors of the light scattering type. Generally, the dust content of flue gases is over the measurable range of the light scattered type stack dust monitor, and therefore the sample of the gas drawn in must be diluted with from 10 to 1000 times by volume of dry clean air. At the same time, th temperature and water content must be decreased. The dulution is done by either of two different means, closed and open types.
The dilution means of the closed type samples a part of flue gases, mixes it with clean (diluting) air being recycled (by a recycling system provided independently of the extracting system), and then extracts the gaseous mixture for an aerosol monitoring instrument. Because of the construction described, the closed type requires, in addition to the filter or filters and the pump for obtaining the clean air, a dehumidifier for removing the drain water as the condensate of the moisture content of flue gases collected gradually as a result of recycling. Inevitably, the closed type apparatus has to be large and heavy.
On the other hand, the open type is free of the system for recycling clean air that is needed by the closed type. It thus need no such means for removing mists and the like from flue gases as is required by the closed type. Naturally, the open type may be smaller in size and lighter in weight than the closed type.
The conventional sampling method of the open type nevertheless has drawbacks in that the variation of the flue static pressure is accompanied by the corresponding variation of the quantity of flue gases being drawn in from the flue to the extractor because the mixed gas after the static pressure variation is directly extracted for the aerosol monitoring instrument and, consequently, the dilution multiple is not kept constant and an error in measurement will result.
Another disadvantage of the conventional method arises from the fact that the flow rate of the sample being extracted for analysis by the aerosol monitoring instrument is constant. If the flow rate is to exactly correspond to a changed flow velocity of exhaust gases, the suction nozzle of the sampling tube must be modified in diameter to maintain synchronized suction. This is impractical and, therefore, control of synchronized suction is next to impossible.